Ribbon helix traveling wave tube



J. R. PIERCE 2,792,519

RIBBON HELIX TRAVELING WAVE TUBE May 14, 1957 Original Filed Jan. 11,1946 INVENTOR -J. R. PIE RCE syn/dag?- A TTORNE Y United States atentif) 2,792,519 RIBBON HELIX TRAVELING WAVE TUBE 'John R. Pierce, BerkeleyHeights, N. 3.,assignorto-Bell Telephone Laboratories, Incorporated, NewYork, N. Y., a corporation of New York 8 Claims. (Cl. 315-35) Thisinvention relates to high frequency electronic-devices of the kind inwhich the electric'field ofa high frequency electromagnetic wave that ispropagated along a suitable transmission path interacts cumulativelywith an electron stream over a distance of many wavelengths.

This application is a division of application SerialNo. 640,597, filedJanuary 11, 1946 and issued as Patent 2,636,948 on April 28, 1953.

One example of a device of the kindtowhich the invention relatescomprises, as illustrated in Fig. l of the parent application, anelongated helix of fine wire that is supported throughout its length inaccurate concentric relation with a rectilinear electron stream'directedalong its axis. The stream velocity is such that'there is cumulativeinteraction between the stream and'the electric field of signalstransmitted through theslow wave transmission path provided by thehelix. More specifically, the signals are applied to the end of thehelix where the unmodulated electron stream enters, and they arepropagated along the helix to a signal output connection at thedownstream end with a velocity substantially equal to that of thestream. The signal efiects an initial-velocity modulation of the streamwith resultant bunching, and there is further cumulative interactionincluding a progressive transfer of power from stream to signal.

One object of the present invention is to provide a high frequencyamplifying device of the kind described that is structurally simple andcapable of sustained stable operation despite severe mechanical shock.

A second object is to provide an improved coupling between a slow wavetransmission path and an associated wave guide.

Still another object of the invention is to provide an improved slowwave transmission path for traveling wave tubes or the like which has abroader frequency band width and higher heat dissipation capacity thanthe wire helix, and which may also provide electrostatic shielding forthe electron stream.

In accordance with a salient feature of the invention, the transmissionpath comprises a relatively wide fiat conductor, or ribbon, arranged asa helix.

More specifically, and in accordance with another feature of theinvention, a relatively heavy conducting ribbon helix is disposededgewise and in contact with a concentric cylindrical conductor. Thisconducting cylinder lends strength and stability to the ribbonconductor, and together they form a continuous helical channel openalong one side to permit interaction with the electron stream.

From another aspect, an important feature of the invention resides in asmooth transition between an input wave guide of elogated rectangularcross section and the ribbon helix transmission line, with the widerside walls of the wave guide merging into respective successive turns ofthe helix.

Other objects, advantages, and features of the invention will becomeapparent from the following detailed Patented May 14, 1957 2 descriptionof theernbodimentillustrated in the accompanying drawings.

In the drawings:

Fig. 1 is a longitudinal section of a traveling wave tube illustratingthe principles of the invention; and

i Fig. 2 is a detailed'view of the coupling between a rectangular waveguide and the fiat ribbon helix slow wave transmission path.

Fig. l illustrates-an electronic device constructed in accordance withthe principles of the invention to obtain cumulative interaction betweena stream of electrons and a signal impressed on a transmission channel.Proceeding to a detailedconsideration of the transmission path, theinput and outputwave guides 3, 4 are continued within the evacuatedenvelopes by means of the slow wave transmission structure formed by theconducting cylinder 6 and the closely spaced turns of the conductingribbon 7. The helical transmission channel within the tube correspondsto the rectangular external wave guide in dimensions, with the exceptionthat one of the shorter side walls is efiectively removed. As may bemore clear- 'ly seen in Fig. 2, this permits transition from theexternal wave guide to internal slow wave transmission circuit withlittle discontinuity, and still provides excellent coupling between thetransmission circuit and electron stream within the tube. This couplingarrangement, with one of the wider sides of the waveguide merging withthe first turn 7' of the flat ribbon conductor, and the opposite waveguide wall merging with the second turn7", has the advantage ofstructural simplicity in addition to its good electric properties.

Returning to the over-all view shown in Fig. 1, the electron streamforming electrodes includes the cathode 8, the electron focusingelectrode 9, accelerating electrodes 10 and 11, and the collector 12.The cathode heater current and the bias for the focusing electrode 9 aresupplied from the voltage sources 13 and 14, respectively. Suitableaccelerating and anode voltages are provided by the high voltage source15. The foregoing electrode arrangement serves to provide a highvelocity electron stream paralleling the slow wave transmissionstructure 6, 7, for amplifying interaction with the high frequencyenergy propagated therein.

In order to suppress undesired oscillations, suitable high frequencyloss material 18 may be placed between adjacent turns of thewave-guiding ribbon 7. This material may be a mixture of ceramic andconducting material or other substance capable of absorbing energy froma high frequency field, and may extend along the waveguiding channelsbetween the turns of the copper ribbon 7 to distribute the loss asdesired. As an alternative, portions of the ribbon 7 may be plated withhigh loss material such as iron, or the attenuation may be obtained inany other desired manner.

Under adverse operating conditions traveling wave tubes can be somewhatsensitive, and mechanical shock as Well as undesired stray electrostaticor magnetic fields may disturb their stable operation. In the deviceaccording to the present invention, however, the ribbon helixconstruction has substantially greater structural rigidity than theconventional wire wound helix. Furthermore, the conducting cylinder 6,in addition to forming the outer wall of each wave-guiding channel, alsoacts as a protective shield against stray electrostatic fields whichmight otherwise deflect the electron stream. In addition, the slow wavetransmission circuit disclosed herein has the ancillary advantage ofhigh heat dissipation which becomes important at high power leveloperation.

In order to shield the tube from magnetic fields, the ferromagneticshield 19 is provided. In place of this shield, a coaxial coil may beemployed to provide a.

strong axial magnetic field to prevent deviation of the electron beam.

the invention. Other arrangements maybe devised by those skilled in theart without departing from the spirit and scope of the invention.

What is claimed is:

1. In a high frequency electron tube, an evacuated envelope, electrodemeans'within said envelope forming a stream of electrons, a cylindricalconductor paralleling said electron stream, and a ribbon conductor inhelix form having one edge contacting said cylindrical conductor, withthe conducting ribbon helix extending from said cylindrical conductortoward said electron stream- 2. An electron tube'as set forth in claim1, wherein input and output wave guides are coupled to said ribbon helixadjacent the two ends thereof.

3. In combination, an evacuated envelope, electrode meanswithin saidenvelope providing a stream of charged particles, a slow wavetransmission path in coupling proximity thereto, said slow wavetransmission path comprising asubstantially cylindrical elongatedconducting body having a partially open conducting helical transmissionchannel on a curved surface thereof, with the open side of saidtransmission channel facing said stream.

4. In'combination, an evacuated envelope, means providing a stream ofcharged particles within said envelope, a rectangular U-shaped helicalchannel of conducting material forming a slow wave transmission circuitadjacent said stream, and input and'output wave guides of substantiallythe same cross-section as said channel coupled j to said slow wavetransmission circuit.

5. The combination as set forth in claim 4 in which the distance acrossthe mouth of said U-shaped channel is less than the depth of saidchannel, whereby a smooth transition may be efiected between the inputand output wave guides and said slow Wave transmission circuit.

6. In combination, an evacuated envelope, electrode means within saidenvelope providing a stream of charged particles, and a slow wavetransmission path comprising a fiat wound conducting ribbon in couplingproximity thereto, with the width of said ribbon being greater than thespace between adjacent turns of said ribbon.

7. A wave amplifying device comprising a transmission path capable ofguiding high frequency electrical Waves, said transmission pathcomprising a hollow wave transmission channel of conducting materialwith a substantially continuous side aperture along at least a portionof its length and which is formed into a helix with the said aperturefacing the axis of the helix, and with the turns of said helix beingclosely spaced so that a single conducting partition separates adjacentturns of the interior of the transmission channel, means to impresswaves to be amplified upon an input end of said transmission path topermit travel of the waves along said path, an evacuated envelope andelectrode means for producing an electron stream along said path in atraveling electric field associated with the said traveling waves and inthe direction of travel of that field, said field being located alongthe axis of said helix, said stream entering said field as asubstantially unmodulated stream, the said transmission path beingcharacterized in that the propagation velocity of the said electricfield is of the same order of magnitude as the velocity of the electronstream passing therethrough whereby energy is transferred from theelectron stream to the said waves along the length of the said pathtraversed by the electron stream, and an output circuit connected to theend of the said transmission path opposite the said input end.

8. In combination, an evacuated envelope, electrode means within saidenvelope providing a stream of charged particles, a slow Wavetransmission path in coupling proximity thereto, said slow wavetransmission path comprising a continuous helical wave transmissionchannel of conducting material and having only conducting materialseparatingsuccessive turns of the transmission channel, with saidchannel being open toward said electron stream.

References Cited in the file of this patent UNITED STATES PATENTS2,122,538 Potter July 5, 1938 2,300,052 Lindenblad Oct. 27, 19422,439,401 Smith Apr. 13, 1948 2,672,572 Tiley Mar. 16, 1954

